1. Field of Invention
The present invention relates to hydrocarbon well control in general and in particular method and apparatus for sealing an open well bore.
2. Description of Related Art
In hydrocarbon production, it is frequently desired to seal or isolate one zone of an oil well from an adjacent zone. In such situations, a sealing element is frequently used to seal and isolate the production string to the main bore or to seal adjacent zones from each other. Such sealing elements may be components of a production packer, an open hole production packer, seal adapter, pressure chamber seal adapter (with charged high pressure chamber on board), a liner hanger packer, a full bore liner top packer, a straddle type stimulation tool, a hybrid type stimulation tools (hydraulic and mechanical packer), a element made from swellable rubber compounds, an open hole seal or a cased hole seal all of which may be mechanically, hydraulically, hydrostatically or pressure chamber operated. Existing sealing elements may be of an open well or a sleeved well type. Such sealing elements may also be utilized to seal the well bore during completion, hydraulic fracturing or reworking procedures. With open well sealing elements, the sealing element is required to engage upon and form a seal with the bare rock or soil wall or formation of the well bore. Difficulties with such open well sealing elements are known to exist.
Conventional sealing elements may include either a swellable or an inflatable sealing element to seal against the bore wall. Such conventional sealing elements have had difficulties achieving a proper sealed between the open bore and a sealing element. Such difficulties have resulted from several factors. One such factor is direction of the expansion of the sealing element. In particular with swellable or inflatable sealing elements, the center of the sealing element tends to racially expand to a greater amount than the edge portions thereof. This difference in swell or expansion of the sealing element provides an angular or tapered exterior surface of the sealing element that may permit a portion of the working fluid within the well bore to engage upon and exert a radially inward pressure upon the sealing element. This radially inward pressure upon the sealing element may be sufficient, at high well pressures to displace the sealing element inwards so as to create or expand a gap between the sealing element and the well bore wall, thereby compromising the seal provided by the sealing element. It will be appreciated that higher pressures, such as experienced during hydraulic fracturing, or facing procedures further exacerbates this problem.
Additional factors which have made conventional sealing elements less useful, is the difficulties with inserting the sealing element into the desired location prior to expanding or otherwise activating the sealing element. Many conventional sealing elements includes a longitudinally movable actuator or driver acting upon the sealing element to radially expand it. During insertion, the longitudinally moving actuator may be prone to hanging up or otherwise being frictionally engaged upon the wall of the well bore. Such friction or hang-up may require the sealing element to have a larger insertion force applied thereto. However, such greater insertion force may also inadvertently actuate or expand the sealing element due to longitudinal movement of the actuator which is gripped by the well bore relative to the remainder of the sealing element. Additionally, it will be appreciated that a sufficiently high enough actuation force must be applied to the sealing element to prevent the hydraulic pressure in the well bore from forcing its way therepast. Previous solutions to inadvertent actuation of the sealing element has been to provide a shear pin between the longitudinal movable actuator and the remainder of the device. Such shear pins must have a preselected shear force. Difficulties have existed in selecting such a shear force to be high enough as to prevent inadvertent actuation as well as to be low enough to still permit actuation of the sealing element.